Recovery of indium



Sept l1 .1945- H. M. ncDRAN ETAL 2,334,610

REcovEnY oF INDIUM Filed uay a. 1940 m mm BY PM Dwi luw. Wina ATTORNEYS Patented Sept. ll, 1945 I RECOVERY F INDIUM Homer M. Doran, Meryl A. Jackson, and Alfred I. Ali', Great Falls, Mont., assignors to Anaconda Copper Mining Company, New York, N. Y., a.

corporation o! Montana Application May s, 194e, serial No. 333,920

7 claims.' (ci. 'z5-121) This inventionI relates to the recovery of indium, and has for its principal object the provision of an improved method for recovering indium. The method of the invention involves a novel combination of steps, many of which are themselves novel procedures for the treatment of indium-bearing materials.

Indium, in nature, is generally found associated with zinc ores, such, for example, as complex lead-zinc ores. In the customary practice of l0 cipally with the treatment of this indium-bearconcentrating such lead-zinc ores, the indium is ing acid leach solution. found largely in the zinc concentrates. Some The usual method employed for the recovery indium follows the lead concentrates, however, of indium from acid sulphate Solutions comprises and indium is therefore found in the lead blast first precipitating the indium from solution as furnace products such as nuedust and lead blast indium hydroxide. This is accomplished by neufurnace slag.` Inthe treatment of the lead blast trallzng the acid solution With a base such as' furnace slag for the recovery of zinc oxide, indium Zinc oxide. The indium hydroxide precipitate is found concentrated in the zinc oxide fume. is filtered away frOm the Solution and dissolved In the hydrometallurgical vtreatment of zinc in sulphuric acid. This dissolution, ltretion ores and other zinc materials for the electrolytic and Precipitation muy be repeated a number of recovery ci' zinc, the ore is rst concentrated. times until E Slllcienl Concentration 0f indium The zinc concentrates are roasted or calcined to is obtained. The indium hydroxide precipitate change the sulphidcs into soluble oxides, and the ls then finally dissolved in Sulphlllic acid. the calcined material is leached with sulphuric acid undissolved portion of the material ltered away to dissolve the zinc and other soluble oxides. The from the solution. and the indium-bearing acid resulting zinc-bearing sulphate solution is 'purisulphatev solution treated with hydrogen sulphide fled to remove those metals .injurious to the elecgas. By suitable adjustment of the acidity of the trolytic deposition of zinc and zinc is recovered soluliOn. any arsenic present in the 50111121011 is from the puriiled solution by electrolytic deposiremoved es arsenic sulphide. By a second adjusttion of the metal on aluminum cathodes, ment of the acidity of the solution, the indium is It is the general practice, although not always precipitated as `indium sulphide. The indium followed, to leach the calcined material in two sulphide precipitate is leached with concentrated stages. In the ilrst leach or stage an excess hydrochloric acid, and the acid chloride solution, of calcine is added as a purifying agent. The after suitable purification, forms the electrolyte excess of zinc oxide is then dissolved in a second leach or stage, and the solution from this stage is added to the acid used in the rst stage. Thus, all of the solution is subjected to the purifying elect of the zinc oxide.

In cases where the calcined material contains only very small amounts of such impurities as arsenic. antimony, germanium, iron, etc., the purillcation treatment with zinc oxide calcine may be eliminated and complete extraction of the zinc may be accomplished in one leach, which bearing zinc calcine or zinc oxide-fume containshould be finished slightly acid. ing impurities including iron and arsenic, but When zinc oxide fumes are treated for the it is understood that the process can be applied electrolytic recovery of zinc, either or the above equally well to the treatment ofany other indiummethods may be used, depending on the amount bearing material in Which the indium Present is of impurities in the fumes. In some cases, vwhere soluble in sulphurlc acid. the amount of impurities contained in the fumes A complete process for the recovery of indium is substantially larger than the amount generin accordance with the method of the invention ally contained in ordinary zinc calcines, it is fromanindium-bearlng material containing zinc advisable to employ only the acid leach. The in acid-soluble form and further containing imimpurities in the acid'leach solution are then` removed by any suitable method before the electrolytic removal of the zinc from the solution.

Indium and the oxldesof indium are soluble in sulphuric acid, forming indiumy sulphate. Therefore, in anyof the above methods for treat.- ing zinc-bearing material, any indium present in the original material will be found in the acid leach solution. Heretofore known methods for the recovery of indium metal are concerned prinfrom which indium metal isrecovered electrolytically. I

The present invention provides an improved method for the recovery of indium from indiumbearing materialsuch as zinc calcines or fumes which avoids the necessity of treating large volumes of leach solution to recover indium present therein in very low concentrations. The method of the invention is described below with par-l ticular reference to Athe treatment of indiumpuritles including iron and arsenic involves nrst to obtain an acid solution containing indium. This solution is treated with a reagent of the group consisting of zinc oxide, sodium bisulphite, and sodium sulphite in such manner as to form an insoluble precipitate containing indium free from the bulk of the iron and arsenic originally present. material is freed, at an early stage in the process and without substantial loss of indium, fromthe greater part of the mineral impurities with which it is associated in the original material. In consequence the recovery of metallic indium of high purity is greatly facilitated.

The indium-bearing precipitate thus obtained may be treated with an aqueous solution of a strong alkali to dissolve aluminum and a further amount of arsenic. After this treatment. the precipitate may be washed with water and decanted. 'I'he precipitate may then be treated with dilute sulphuric acid in such manner as to dissolve at least a portion of the remaining zinc without acidiiying the precipitate. It is important that the precipitate be not acidied, or the indium will dissolve and the benet of the alkali treatment and the dilute `sulphuric acid wash will, to a large extent, be lost.

After completion of the dilute sulphuric acid treatment or wash, the indium-bearing precipitate is dissolved in a relatively strong acid` solution, and this strongly acid indium-bearing solution is treated with a sulphide such as hydrogen sulphide gas sol as to precipitate substantially all of the remaining arsenic. The precipitated sulphides are separated from the residual solution and the resulting arsenic-free solution is treated with metallic zinc, whereby metallic sponge indium is precipitated. It is important that all of the arsenicfbe eliminated from the solution prior to treatment with metallic zine so as to avoid danger of the formation of extremely poi' sonous arsine sas.

'I'he sponge indium obtained by treatment of the solution with metallic zinc is then treated for the recovery of metallic indium in commercial form. Although this may be accomplished in a number of ways, the present invention contemplates two novel procedures for this Purpose. either of which may be employed depending upon thedesired purity oi' the indium metal recovered.

Y Ii' metallic indium of ordinary commercial purity is satisfactory, the indium sponge obtained from Vthe treatment with metallic zine may be melted in a suitable vessel beneath a coverof a fused strong alkali. The fused alkali cover prevents oxidation or the molten indium and further ef fects some additional puriiication of the metal during melting. The molten indium is cast from the melting vessel into suitable shapes for the market.

If, on the other hand, it is desired to produce metallic indium of very high purity, the sponge precipitated by the metallic zinc is dissolved in hydrochloric acid. The resulting solution of in- In this manner the indium-bearing dium in the form of a chloride is then treated, advantageously with barium chloride, to precipitate sulphate ions, which if present in any appreciable amount would interfere with subsequent recovery of pure indium by electrolytic means. 'Ihe sulphate-free solution may be treated with a sulphide under suitable-conditions as to acidity so as to enect precipitation of a further quantity of impurities, such as cadmium, and the precipitate thus formed may be separated from the residual solution. l

'To eliminate4 last traces of impurities from the solution, the indium-bearing solution is introduced into an electrolytic cell fitted with a cathode and. a soluble anode, advantageously an anode of indium metal. The solution in the cell is subjected to the action of an electric current of such current density and at such applied voltage as to overcome polarization and effect deposition of impurities at the cathode without substantially depleting the solution of indium and without causing deposited impurities tobe redissolved.

After substantially complete purification of the solution in this manner, the solution is withdrawn from the electrolytic cell and separated from any slimes that may have formed. The purified solution is introduced itno a second electrolytic cell iltted with an anode and a cathode. each advantageously composed of graphite, and is there subjected to the action of an electric current at sumciently high current density and applied voltage to overcome polarization and to effect deposition of metallic indium of high purity at the cathode. The indium metal so deposited is stripped from the cathode, melted, land cast into suitable shapes for the market.

The invention will be better understood from the following detailed description of the complete process, considered in conjunction with the accompanying ilowsheet.

The ilrst step in the new process for the recovery of indium from indium-bearing calcines, zinc oxide fumes or other indium-bearing material is to treat the material with dilute sulphuric acid in such a way as to dissolve practically all of the zinc and other soluble oxides, and to leave all of the indium undissolved in the leach residue. This is accomplished by maintaining the acidity o! the leach solution at from l to 3 g./1. H2804. At this acidity, indium is either insoluble in sulphuricacid, or it is precipitated from the arsenic and iron would be precipitated and accompany the indium. The acid zi'nc sulphate solution from this leach is separated from the unleached material by settlement and filtration according t0 the usual practice, and is treated in the usual manner for the electrolytic recovery of its zinc content.

'I'he indium-bearing residue from this leach, which also contains insoluble substances such as lead compounds, is treated with relatively strong sulphuric acid' to dissolve the indium and whatever other soluble substances are present. This is accomplished by 4adding sulphuric acid to the residue until the acidity of the solution reaches 20 to 25 g./l. HsSOi. At this acidity, the maximum amount of indium has been dissolved. If the acidity of the leach is brought up gradually to from 20 to 25 g./l. HiSO, part of the arsenic and iron which is in the residue will not" be dissolved but will remain in the undissolved portion of the residue. This latter method o! leaching is particularly advantageous when the original indium-bearing material contains arsenic and iron. When this leach is completed, the acid sulphate solution is separated from the undissolved residue by settlement or illtration or both.

The acid sulphate solution from the above-described leach' contains all of the recoverable indium present in the original indium-bearing material. The iirst step in the recovery of this indium may be in accordance Awith any one of thev three following procedures.

Procedure A.Zinc oxide is added 'to the indium-bearing acid sulphate solution until the acidity of the solution has been reduced to from 1 to 2 g./l. H2804. At this acidity, substantially all of the indium is precipitated as indium hydroxide, a minimum of zinc is assured in the precipitate, and part of the arsenic and iron still present remains in th'e solution and so may be separated from the indium. The indium hydroxide precipitate is separated from the bulk of the solution by settlement and decantation, after which the residual solution is separated from theprecipitate by filtration. It is desirable to heat th'e solution before ltration to facilitate the filtering operation. The indium precipitate is now ready for further treatment.

.Procedure 1st-The indium-bearing acid suiphate solution is treated 'with a base, such' as zinc oxide, until theacidity is reduced to from '1 to 5 g. /l. H2804, whereupon sodium bisulphlte is added in quantity sufficient to precipitate the in-f dium as basic indium sulphite (In2(SOs) s.In(OH) 35H20) The addition of the sodium bisuiphite to the acid solution causes the generation of sulphur dioxide gas,'and this gas will reduce all of the iron and a large portion of the arsenic. When arsenic and iron are in a reduced state, th'ey will not be precipitated, with the indium, especially when the' phate solution is treated with sodium sulphite in sulcient quantity to reduce the acidity of the solution to from 1 to 3 g./1. H2804- Whenthis acidity has been reached, the solutionis treated with a base such as zinc oxide until the solution precipitation with the indium. After the addition of the sodium sulphite, the solution is heated to about 85 C. When precipitation of the indium has been accomplished, the precipitate is separated from the solution by filtration and is ready for further treatment. l

Theprecipitate obtained by any of the three above-described procedures is treated by a leaching 'operation with concentrated sodium hydroxide solution, one-half pound of sodium hydroxide being added to each dry pound of precipitate. The sodium hydroxide dissolves a large proportion of the arsenic remaining in the precipitate as well as any alumina that might have been precipitated, but it does not aifect the indium. The

indium therefore is further concentrated, concentrations of as high as 30% indium having been obtained.- The sodlumhydroxide leach is allowed to settle and the leach solution is decanted.

The leach residue is given several water washes to insure removal of most of the caustic solution. After the residue from the caustic leach has been washed suillciently, it ls treated with. dilute sulphuric acid, sulllcient acid being added to dissolve any zinc hydroxide th'at may have been precipitated by the addition of the .sodium hydroxide. Extreme care must be used to insure that at no time will the pulp become even slightly acid, because the indium in the pulp is in a very acid-soluble form, and only: a trace of acid will cause a loss of indium. If the neutral point is passed and the pulp becomes acid, this acid must be neutralized, which means that an excess of leach, or the elimination of any zinc from the acid wash, would be lost. After the acid wash is completed, the pulp is iiltered away from the solution and the iiltered pulp is treated further for the recovery oi' indium.

The indium which has been concentrated in the pulp from the sodium hydroxide leach and sulphuric acid Wash' is dissolved in commercial sulphuric acid. The acidity of this leach is maintained at from 70 to 100 g./l. HzSOi to insure maximum dissolution of the indium. After the indium has been dissolved, the undissolved Procedure C."I'hev indium-bearing acid sulhas become neutral, but not basic. It may be f desirable to have about lg./l. lH1804 remain in solution. The action of the sodium sulphite is similar to thatA of Jsodium bisulphlte. Sodium sulphite, however, is more basic in its reaction than the bisulphlte, and consequently its tendency to neutralize-the acid sulphate solution is stronger. Control of the acidity oi' the solution is therefore an important point. The indium is probably precipitated as the basic indium sulphite as in Procedure B. Addition of the sodium sulphite to the acid sulphate solution generates sulphur dioxide gas which eectively reduces any iron and arsenic present and prevents their solids are illtered away from the solution and treated for lead and other metals not soluble in the acid. The acid sulphate solution containing the indium is treated further for the recov- Yery of th'e indium.

Up to this point in the process, if all of the necessary precautions have been observed," a portion of any arsenic and iron which was present in the original indium-bearing maferial will be present in the strong acid sulphate solution. There will also be present in varying amounts such impurities as copper. antimony.'

germanium, etc.. which must be removed before the final recovery of indium. The acidity of the strong acid sulphate solution is therefore adjusted by the addition of more sulphuric acid to bring the acidity up to a point where the arsenic and other metals may be precipitated as sulphides while the indium remains unprecipitated in the solution. An acidity between 120 and 150 g./1. H2804 is usually sumcient for this precipitation operation. Hydrogen sulphide gas is then passed into the solution to eiTect precipitation of arsenic and other impurities as sulphides. After th'e arsenic has been completely-removed, as determined by actual test for its presence in the solution, the sulphide precipitate is separated from the arsenic-free indiumbearing solution by illtration.

The arsenic-free acid sulphate solution containing the indium is now treated with metallic zinc for the removal oi.' the indium. The solution should be arsenic-free when the zinc metal is added for otherwise extremely poisonous ariication operation so as to secure most effective and repeated use of the purifying metal. The area of the electrodes should be relatively large,

and the solution should be agitated during treatsine gas will be formed. The optimum temperature for the replacement of indium by zinc has .been determined to lie in the range from 30 to 50 C. The acidity of the solution should be high to start with, say from 100 to 150 g./l. H2804, to insure the removal of any zinc oxide on the surface of the zinc metal. The indium in the acid sulphate solution is precipitated as a high-grade indium metal sponge containing about 96% indium This sponge is separated from the solution by filtration and is washed thoroughly with water to remove any occluded water-soluble zinc, iron, etc., and is then thoroughly dried.

Assuming it is desired to recover metallic indium of high purity from the dried indium sponge.' the sponge is now treated with hydrochloric acid to dissolveI the indium. The acidlty'oi this leach is maintained at as low a concentration as possible and still secure a high concentration of indium in the solution. -Leaching 'with a solution containing ka low concentration of acid and using an excess of indium sponge insures minimum dis` solution of the more insoluble impurities that might be present in the sponge.

The acid indium chloride solution from thisleach is separated from the undissoived solids by filtration. The acid chloride solution -is then treated with a saturated solution of barium chloride to remove any 'S04 ions that may be present` in the solution. All S04 ions should be removed, inasmuch as the presence of these ions is injurious if present during the final electrolysis of the indium chloride solution.

The barium sulphate precipitate is removed from the acid chloride solution by illtration and the acidity of the solution is reduced to from 8 to l g./l. HCl by the additionof. a suitable base such as sodium hydroxide. The solution is then treated with hydrogen sulphide gas to remove any cadmium and copper and a portion of any lead that might still be present. The solution is then separated from the sulphide precipitate.

The acid indium chloride solution still carries small amounts of impurities such as lead, tin, etc., which will deposit with the indium during electrolytic recovery thereof if they are not removed from the solution. No eliective way has been found to remove these last traces of impurities except -by electrical purification. 'I'he acid indium chloride solution is introduced into an electrical purification cell which is tted lwith soluble anodes, preferably of indium metal, and cathodes which may be made of graphite or of the same metal as the anode. Direct current is applied to the cell withl a current density sumciently high and 'at a potential of suilicient value to' overcome polarization and force the deposit of impurities, but the current density and potential should not be high enough to dissolve any impurities from the anode orl to deplete the solution of indium to any substantial extent. When usingindium anodes and'cathodes, a practical current density is 2.5 amperes per square foot of anode area and a practical applied potential is 1 to 2 volts. When both anodes and cathodes are made of the same metal such as indium, the polarity of these electrodes may be reversed from time to time during the course of the puriment in the cell in such a manner as to insure complete deposition of all impurities in a short period of time. This time generally varies from two to four hours. When the impurities have been removed from the solution, as determined, -for example, by spectroscopic tests, the solutionis filtered away from the slimes or other solids accumulated during the purification. Inasmuch as these solids contain some indium, they are ad-y vantageously retreated for the further recovery of the indium. The filtered acid indium chloride a solution is now ready for electrolysis.

Electrolysis of the acid indium chloride solution advantageously is accomplished in a suitable cell equipped with insoluble graphite electrodes. Direct current is applied at a current density of from 1 to 15 amperes per square foot of cathode area. The best deposit is obtained at a current density of approximately four amperes per square foot and -a terminal voltageof approximately 2.0

volts.

The cathodes are removed from the cell at suitable intervals and am7 residual electrolyte is washed .with -water from the surface of the cathode deposit. 'I'he indium metal is stripped from the surface of the cathode and the cathode replaced in the cell for further deposition of indium. 'I'he electrolyte may be depleted to as low as 0.02 g./1. indium, but in practice, it is desirable to finish electrolysis when the indium content of the electrolyte has been reduced to from 8 to 1,0 g./l. indium. The indium, thus left in the electrolyte is returned to the process for eventual recovery.

The metallic indium stripped from the cathode is dried, melted andv cast into suitable shapes in accordance with usual practice. The indium metal produced by the above process has a. purity of 99.99+% indium. rf this nighpurity of indium is not required, but a. purity of say 99.8 to 99.9% indium is sufllcient, the abovedescribed steps following the precipitation of the indium sponge may be dispensed with and direct melting of the indium sponge may be substituted, as outlined by the optional procedure shown in dotted lines on the accompanying ilowsheet. This is accomplished by rst briquetting the indium sponge and then melting it under a cover of a f ed strong alkali such as sodium hydroxide. dium, being a soft and ductile metal. is easily briquetted.

Sodium hydroxide or other suitable caustic is melted in a suitable receptacle such as a. cast iron pot and the indium sponge briquettes are added to the molten caustic. The density of indium is greater than that of the sodium hydroxide and the inetal therefore drops to the bottom oi the receptacle. The cover of caustic prevents oxidation of the metal and also dissolves some of the lzinc and lead in the sponge. When the indium sponge is melted, the molten metal is poured out and cast into suitable shapes. I'he caustic, which will contain some indium, is returned to the Proc.-

' 7; is understood that theprocessv may be applied also n indium-bearing material con f" `p le masacre to other indium-bearing materials. It is also understood that the various novel steps of the complete process each are individually applicable to the treatment of appropriate indium-bearing residues or solutions without departure from the scope of the invention.

We claim:

i. In the method oi recovering indium 'from induim-bearing material containing ainc in acid-v soluble form and lui-ther containing impurities including iron, aluminum and arsenic wherein the material is leached with a very dilute acid so lution in such manner that the bulk of the aine is dissolved and the indium remains in the undissolved residue and the indium-bearing residue is separated from the leach solution and dissolved in relatively strong acid to obtain enl acid .solution containing indium, the improvement which comprises treating the resulting indium=bearing solution to form an insoluble precipitate contg l indiumiree from the bulls oi the iron and arsenic originally present, treating the indiun1=bearins precipitate thus obtained with n solution oi a strong alkali to dissolve aluminum and a further amount of arsenic therefrom, further treating the precipitate with dilute sulphuric acid in auch manner as to dissolve aine therefrom without acldii'ying and dissolving indium from the precipitate, separating the thus=treated indium-bearing precipitate from the solution, .1 imlving the seperated precipitate in e. relatively strong acid solution, treating the acid solution with a sulphide to precipitate substantially all remaining arsenic therefrom, separating the resulting sulphide precipitate from the solution, treating the arsenic free solution with metallic zinc, whereby metallic sponge indium is precipitated, and recovering metallic indiumrrom the precipitated sponge.

2. In the method of recovering indium from in'- dium-bearing materia1 containing zinc in acidsoluble form and further containing impurities furie acid solution having an acidity corresponding to about l to 3 g./l. H2804 -in such manner that the bulk of the zinc and considerable amounts oi arsenic and iron are dissolved and the indium remains in the lindissolved residue-separating the indium-bearing residue from. the zincbearlng solution, and dissolving the indium-bearing residue in a relatively strong acid to obtain an acid, relatively -concentrated indium-bearingl so lution. L l

e. In a method for the recovery oi indium from indium-bearing material containing zinc in aciclfa soluble form, the steps which comprise leaclra ing said material with a dilute sulphuric acid solution having an acidity corresponding to about i to 3 g./l. H2804 in such manner that, the bulls oi the zinc is dissolved and the indium remains in the undissolved residue, separating the indiumbearing residue from the zinc-bearing solution and dissolving the indium-bearing residue in al relatively strong sulphuric acid solution having n residue.

` ilcient amount to reduce the acidity o! the salue including iron and arsenic wherein the material is leached with a very dilute acid solution in such manner that the bulk oi the zinc is dissolved and the indium remains in the undlssolved residue and the indium-bearing residue is separated from the leach solution and dissolved in relatively strong acid to obtain an acid solution containins indium, the improvement which comprises treat@ ing the resulting indium-bearing solution to form an insoluble precipitate containing indium free lfrom the bulk of the iron and arsenic originally present, subsequently dissolving the indium-bearing precipitate in a relatively strong acid solution, treating the resulting solution with a sulphide in such manner as to effect substantially complete precipitation of residual arsenic therefrom, separating thepreciplite from the indium-bearing solution, treating the substantially arsenic-free 'indium-bearing solution withv metallic rino,

lwhereby metallic sponge indium is precipitated, and ering metallic indium from precipitated 8. in a method-for the ery of indium from zinc, arsenic wat in scidQsoluble iorm, -the steps which f said al with a dilute sultion to a value corresponding to about l -to S g./l. H9804, and treating the resulting solution with zinc oxide in sumcient Vamount to render the solution subantially neutral but not basic, whereby the indium is precipitated from. the solu-u tion as an insoluble compound substantially vtree trom the bulk ci the iron and arsenic orilly presentand-separatlngthe indium-bearing cipltate irorn the residual solution.

li. En a method for recovering indi involving treatment or an acid-soluble indiuniebes material containing a relatively high concentra tion of indium associated with impurities including arsenic, the steps which comprise dissolving said material in a relatively strong acldto pro= duce an indium-bearlng-- solution containing arsenic and having an 'acidity corresponding to at to 150 g./1. H2804, treating the acid solution thus obtained with a sulphide in such manner as to eiiect substantially completepre cipitation of the arsenic, separating the sulphide precipitate from the indiumebearins solution. and

treating the indium-bearing solution with metalllc cinc, whereby metallic sponge indium is precipitated from the solution.

nouns. M. mn. .e JAexsoN. Armen I. Au'. Y 

